Devices that utilize rechargeable batteries and solar panels for charging the batteries are useful in underdeveloped and developing countries and in remote areas where there is no reliable electric power grid system available. Alternative power sources for lighting, powering, and recharging devices are needed more than ever because of the modern proliferation and reliance upon electronic devices for communication.
Such systems typically have set, inflexible designs that include only a specific solar panel or set of solar panels and a specifically designed battery or a specific type of battery. The designers of such systems often constrain the design, making it easier to implement. Thus, the purchaser or user of such systems typically has no options for expanding, changing, or adjusting such systems. Such systems typically have a specific, custom solar panel. This allows the designer to dictate the exact voltage and current input to the circuit. However, this eliminates choice and upgradeability for the consumer. For instance, to control the cost of the product a designer may choose to provide a low power solar panel with the product, which works well in regions of the world with high incidence of solar radiation. If that product is sold where cloud cover is common or there are other causes of low solar radiation, the custom solar panel will not produce enough energy to properly power the unit. And because the solar panel is custom to that specific product, adding another solar panel to the product or changing the panel to a higher power solar panel to increase the power input to the circuit is often not an option for the consumer.
Such systems or products are also often designed around one battery type, requiring the purchaser to replace the batteries with the same type of batteries as needed. Some products will accept third party primary (non-rechargeable) or secondary (rechargeable) batteries of standard sizes that can be purchased from various sources. However, the user of the system or product may be confused because of there may be several different battery chemistries available within the same battery package size (e.g., AA, AAA, D, etc.). Consequently, systems limited to a single battery chemistry create a risk that the user will install batteries having chemistries that are incompatible with the system, which may result in system malfunction. Malfunctions can occur by installing batteries having a voltage that is too high or too low for the design of the system. Malfunctions can also occur if the product is designed to recharge secondary batteries, but primary batteries are improperly installed. In addition, the wrong type of secondary batteries (with the wrong chemistry) can damage the unit when they are installed because the system will apply its standard charging algorithm, which may be incompatible with the battery chemistry. A purchaser may even install several different types of batteries within the same unit, compounding these same issues. Thus, when the designer constrains the design to one specific battery type, the risk of product failure due to installation of the wrong battery type is then transferred to the purchaser, who is likely unaware of the risk.
Other manufacturers may eliminate the risk that the user will install the wrong batteries by designing a custom battery pack that is unique to the product. The custom battery pack may or may not be replaceable. If the battery pack is not replaceable, the product is unfortunately discarded when the batteries no longer function, which results in waste of materials and costs. In other cases, the product may be designed to allow for the replacement of the custom battery pack when the battery pack no longer functions. Because custom battery packs are arranged and installed in the product in specific configurations and the product is not designed to charge one battery at a time, but rather the entire custom battery pack, the batteries are charged in an unbalanced and inefficient manner that results in a relatively short battery life for the custom battery packs and forces the consumer to purchase a new custom battery pack after relatively few charge-discharge cycles (referred to as “cycle life”). Typically, the custom battery packs are only available through the manufacturer who sells the custom replacement batteries to the consumer, or through 3rd party vendors selling knock-offs that are often inferior and/or unreliable.
Consumers may not understand that all batteries (primary and secondary, and custom battery packs) fail over time. Because it is often not obvious to the consumer how to replace the batteries, the product is just set aside or thrown away, which may result in the consumer faulting the designer with creating a “cheap” product. For the consumer that understands that all batteries will eventually fail, there are other disadvantages to this design method. The need for a manufacturer or authorized agent to replace the batteries can put an undue hardship on the consumer, especially those in remote areas which have the greatest need for battery-powered products. Also, “custom” battery packs eliminate or reduce the likelihood of competition for the supply of replacement batteries for the manufacturer's product, likely resulting in higher costs for the replacement battery and the product.
The battery design choices made by the product manufacturers are driven by the power requirements of the device, the battery chemistries that are currently available, the risk of damage to the particular product that would result from installation of the wrong battery type, and other factors. Once the manufacturer determines the appropriate battery type, required current, and required voltage, the designer then devises a way for the batteries to be installed in the product. The batteries will be configured in series, or parallel, or perhaps a combination of both. Due to the constrained design, the batteries will always be installed in the same arrangement so that the proper voltage and current are achieved for the product. As already noted, the designer will often choose to provide a custom battery pack with the configuration determined at the factory, and so that they cannot be changed by the consumer.
The battery configuration chosen by the manufacturer may be optimized based on its discharge and charging characteristics. Since the battery's longevity depends on the output current, one battery configuration may be best for charging life of the battery pack. But based on the input power being used to charge the batteries, a different configuration may be best for charging. Since the user cannot be relied upon to change the physical configuration of the batteries based on the batteries being used to supply power versus when the batteries are being charged, the designer is forced to compromise one for the other when setting a single battery configuration.
There are many different battery chemistries available to device manufacturers, For example, the AA and the size-compatible 14500 battery packages may be made to utilize primary, such as zinc-carbon (dry cell), zinc-chloride, alkaline, or lithium chemistry; or a secondary chemistry, such as NiCd, nickle-metal hydride (NiMH), NiZn, LiFePo4, or lithium ion chemistry. The different chemistries all have different strengths and weaknesses, and all have different monetary prices to the purchaser. Of the secondary type, different chemistries yield different amounts of recharge cycles (the literature reports anywhere from 200 recharge cycles to 2000 recharge cycles, depending on the chemistry). Also, different chemistries yield different output voltages, ranging from 1.2V nom to 3.7V nom. Different chemistries may also be best used with different discharge rates (the literature reports recommended discharge rates anywhere from 80 mA to 500 mA). In addition, as a battery is used to provide current, its voltage drops overtime in a way that is uniquely characteristic to its chemistry. Because of the variations in the characteristics of the different chemistries, it is standard practice for designers to first choose a specific battery chemistry in order to simplify the product design. Once the designer has determined the battery chemistry, the number of battery cells and their configuration (series, which adds voltage, or parallel, which adds current) must be selected, taking into account the overall range of voltage through the entire discharge curve of the particular battery type. These factors must be balanced with expected life of the battery and cost of the battery. These design choices result in a specific and constrained design. Often, the chosen design does not satisfy the preferences of all consumers, and thus may alienate a certain portion of the market.
There are particular markets in which the availability of power sources, including batteries, is limited and presents a significant economic burden to the local population. Solar power has been promoted as a potential power source for these underserved regions, but power storage for use in dark and night conditions is necessary to provide a consistent power source for such regions. Systems that are limited to specific battery chemistries can present a problem for the populations in these remote areas because batteries may be relatively scarce and the specific battery type required by the system may not be available. Thus, there is a need for systems that are able to accommodate multiple power and battery options.